Delta Keyframes, how to use
Delta transforms are used when you have some incorrect location in your animation, like if your animated object is at wrong place you can just adjust the location in Delta Transform.
If you don't use Delta transform for such repairing, you have to edit a particular keyframe by overwriting them.
For example, if you have a plane on which a cube is floating from one place to another, you will obviously make a Location keyframe by pressing I. But the problem arises when you want the same animation for another. Dupicate the animated cube at another place, and play the animation, you can't see the another cube in animation, you can see only one cube. Did it disappear?
No, it is just on the location where the original cube is lying during the animation.It has the same Location path which the original cube has, as it is been duplicated!
To fix this, you should use Delta Transform, assume that you duplicated the cube on X axis, now the path should move parallel to the original cube i.e on Y axis, but not on same X axis, so change the location of X axis in Delta Transform, and you'll get the parallel movement of both cubes i.e without affecting your animation movement.
What you will do in absence of Delta Transform?
As I mentioned above, you have to overwrite each keyframe by changing its location again and again by pressing I and selecting Location keyframe, depending upon the number of keyframes you have created. But this makes it easy if you want to change the initial location of any axis and make it permanent till the last keyframe. It will have the same animation but on different axis, which you have changed in Delta Transform.

Also Refer this.